1. Field of the Invention
The present invention relates to a full charge sensing apparatus and a full charge sensing method.
2. Background of the Invention
In the related art, determination of whether a secondary battery has reached a fully charged state is carried out by determining whether or not an SOC (State of Charge), which is a charging rate, has reached 100%. Such an SOC-sensing method may be, for example, a method as disclosed in Japanese Laid-Open Patent Application No. 2005-091217 in which a stable voltage OCV (Open Circuit Voltage) of the secondary battery is measured and an SOC is predicted from this OCV.
Japanese Laid-Open Patent Application No. 2008-145349 discloses a technique in which, since SOV=100% does not always hold at the time the OCV is measured, in order to deal with such a case, a change in SOC after the measurement of OCV is computed by hour integration based on a continuous observation of an electric current.
With the technique disclosed in Japanese Laid-Open Patent Application No. 2005-091217, a fully charged state is determined based on a correlation between OCV and SOC, and the correlation between OCV and SOC varies depending on a type of the secondary battery. Therefore, for example, as in the case of a lead-acid battery of automobiles where a product arbitrarily selected from a group of products supplied from various manufactures by a user is used, there may be a case in which the fully charged state cannot be determined accurately.
With the technique disclosed in Japanese Laid-Open Patent Application No. 2008-145349, in order to compute a change in SOC caused by the entering/exiting of the electric current into/out of the secondary battery, it is necessary to compute a ratio of an amount of entry/exit against a capacity of the secondary battery. However, there may be a case where the fully charged state cannot be determined accurately, since an individual difference and a sensing error exist for this capacity.
Therefore, an object of the present invention is to provide a full charge sensing apparatus and a full charge sensing method capable of accurately determining the fully charged state regardless of the type of secondary battery.